This proposal examines how children and adults develop intuitive understandings of the world around them given clear evidence of the incompleteness of their knowledge. Much of the proposal is concerned with how children and adults track causal structures and use them to make inferences about categories. One set of studies examines links between children's intuitive notions about the world and their understanding of how knowledge is clustered in the minds of others. They will show that quite young children use their ideas of how the world sorts itself into patterns of regularities to make inferences about how one piece of knowledge might entail another, or the division of cognitive labor around them. This way of clustering knowledge is then compared to other ways, such as around a common goal and the developmental tension between the two is explored. A second set of studies examines how children and adults evaluate the quality of their own knowledge and that of others, revealing a powerful "illusion of explanatory depth" in which people think they know how their world works in far great detail than they actually do. The studies further show how this illusion is much stronger for explanatory forms of knowledge than forms such as knowledge of procedures or narratives and they explore how the specificity of this illusion emerges in development. Other studies in this set look at other ways children evaluate explanations for quality while grasping only few details of the explanation. Finally, a set of studies explores various ways in which children are sensitive to causal patterns that might given them a skeletal or framework kind of knowledge within which more precise notions of mechanism can further develop. [unreadable] [unreadable]